digestive system

ANAT3651

Alimentary canal or GastroIntestinal (GI) tract includes…

mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus.

Accessory organs

assist in digestion of food but NOT required. includes teeth, tongue, gallbladder, salivary glands, liver and pancreas.

Purpose of the digestive system

acquire nutrients and water.

alcohol and asprin are absorbed through

stomach

Glucose, lipids, and amino acids are absorbed through

the small intestine

vitamins, water, and minerals are absorbed through the

Large intestine

absorbed nutrients are passed to…

veins of digestive system and then to liver

Fats are absorbed through the ______ and passed into _______, then transported to ____.

small intestine; lacteal ducts; veins of circulatory system

sigmoid colon

storage for feces

6 essential food-processing activities of the Digestive System

1. Ingestion (taking food in mouth)

2. Propulsion = swallowing (voluntary) and peristalsis (involuntary movement of food)

3. Mechanical digestion = chewing, churning food in stomach, and segmentation (Occurs in the mouth, stomach and small intestine).

4. Chemical digestion (breaks down the food material to molecules). (Occurs in the mouth, stomach, and small intestine.)

5. Absorption = transporting nutrients, electrolytes, and water into veins; and fats into the lymphatics.

6. Defecation = elimination of indigestible substances

Peristalsis versus Segmentation

The intestine contains circular and longitudinal smooth muscle.

Peristalsis is a wave-like muscle contraction that moves food along the digestive tract (through the lumen), while segmentation involves contraction to mix food contents.

Histological organization of the Digestive System:

1. Mucosa (true epithelium + lamina propria + muscularis mucosae)
   - Note: Epithelium is either stratified squamous or simple columnar.

   2. Submucosa - contains arteries, veins, nerves, lymphatics, sometimes mucus glands
      3. Muscularis externa - smooth muscle (inner circular layer + outer longitudinal layer)
      4. Serosa (mesothelium) or adventitia

Submucosal nerve plexus

signals submucosal glands to secrete and muscularis mucosae to contract.

Myenteric

-located between the circular and longitudinal layers of muscularis externa
- controls peristalsis and segmentation.

4 types of mucus membranes

a. Protective - stratified squamous epithelium

- Found in the oral cavity, pharynx, esophagus and anus

b. Secretory - simple columnar epithelium

- specialized for secreting mucus

- Found only in the Stomach as Mucus-secreting cells and mucus-neck cells

c. Absorptive (Nutrients) - Simple columnar cells

- modified with increased surface area for absorbing nutrients – found in the small

intestine

d. Absorptive (Water & Electrolytes) - Simple columnar cells

- for absorbing water and electrolytes

- found in large intestine

- will switch to stratified squamous in anus.

alveolar ridge

The line between the tooth and gum

Vestibule

the space between the lip and the alveolar ridge.

labial frenulum, or frenulum of the lip

lip to the gum

lingual frenulum

tongue to floor of oral cavity

uvula

dangles from soft palate

palatoglossal arch

palate to the tongue

palatopharyngeal arch

palate to pharnyx

palatine tonsil

located in between the palatopharyngeal and palatoglossal arches

Filiform papilla

pointed cones on tongue, most numerous and no taste buds,

Fungiform

papillae on tongue with taste buds, round in shape (mushrooms)

Circumvallate

papillae surrounded by a wall, possess taste buds.

sulcus termanalis

separates circumvallate papilla and lingual tonsil.

fauces

opening between the oral cavity and the oropharynx. Borders are palatoglossal arch, uvula, and sulcus terminalis.

tonsilar ring

ring of protective tonsils in the oropharynx (palatine and lingual tonsils)

parotid gland

serous cells secrete amalyse and lysosomes.

sublingual

mucus cells secrete mucus for lubrication

submandibular

serous and mucus cells secrete

Types of teeth (2123)

2 incisiors, 1 canine (cuspid), 3 bicuspid (premolar), and 3 molar

esophagus

carries bolus from oral cavity to stomach. transitions from skeletal muscle to smooth.

type of esophagus epithelium

Stratified squamous epithelium

external layer of esophagus

adventitia not serosa

Inferior vena cava passes through

respiratory diaphragm (caval foramen) at level of thoracic vertebra 8

esophagus passes through

diaphragm (esophageal hiatus) at the level of thoracic vertebra 10 (T10)

cardiac sphnicter

Muscle fibers of the respiratory diaphragm that serve as functional sphincter muscles of the esophagus

Lower esophageal sphincter

The inner circular layer of muscularis externa functions as the sphincter muscle of the

esophagus.

aorta passes through

the respiratory diaphragm at T12

stomach is a site for

chemical and mechanical digestion

regions of the stomach

cardiac, fundus, body, pyloris, greater and lesser curvature, rugae,

pyloric sphincter

prevents food from leaving the stomach. Formed by thickened middle circular layer.

3 layers of the muscularis externa

innermost oblique, middle, circular, and outer longitudinal

what type of cells line the gastric pits?

simple columnar